Internet Explorer Dynamic OBJECT tag and URLMON sniffing vulnerabilities

Advisory ID Internal

1. Advisory Information

Title: Internet Explorer Dynamic OBJECT tag and URLMON sniffing vulnerabilities
Advisory Id: CORE-2009-0625
Date published: 2010-02-03
Date of last update: 2010-02-03
Vendors contacted: Microsoft
Release mode: User release

2. Vulnerability Information

Class: [CWE-497], [CWE-501], [CWE-612]
Impact: Security bypass
Remotely Exploitable: Yes
Locally Exploitable: No
Bugtraq ID: 38055, 38056
CVE Name: CVE-2010-0255, N/A

3. Vulnerability Description

This advisory describes two vulnerabilities that provide access to any file stored in on a user's desktop system if it is running a vulnerable version of Internet Explorer. These vulnerabilities can be used in attacks combined with a number of insecure features of Internet Explorer to provide remote access to locally stored files without the need for any further action from the victim after visting a website controlled by the attacker. The vulnerabilities are simple variations of bugs disclosed previously in CoreLabs Security Advisories CORE-2008-0103 [1] and CORE-2008-0826 [2]. Exploitation of these vulnerabilities requires enticing users to click on URLs otherwise visit a malicious website controlled by the attacker but no further user interaction is needed. As a result an attacker would gain the ability to read any file stored on the user's desktop system but will not be able to fully compromise it to execute arbitrary code without restrictions.

4. Vulnerable packages

  • Internet Explorer 5.01 SP4 on Windows 2000 sp4
  • Internet Explorer 6sp1 on Windows 2000 sp4
  • Internet Explorer 6sp2 on Windows XP sp2
  • Internet Explorer 6sp2 on Windows XP sp3
  • Internet Explorer 7 on Windows XP sp2
  • Internet Explorer 7 on Windows XP sp3
  • Internet Explorer 7 on Windows Vista sp1
  • Internet Explorer 7 on Windows Vista sp2
  • Internet Explorer 7 on Windows Server 2003 sp2 if Protected Mode if OFF and not using Enhanced Security Configuration
  • Internet Explorer 7 on Windows Server 2008 if Protected Mode if OFF and not using Enhanced Security Configuration
  • Internet Explorer 8 on Windows XP sp2
  • Internet Explorer 8 on Windows XP sp3
  • Internet Explorer 8 on Windows Vista sp1 if Protected Mode if OFF
  • Internet Explorer 8 on Windows Vista sp2 if Protected Mode is OFF
  • Internet Explorer 8 on Windows 7 if Protected Mode if OFF
  • Internet Explorer 8 on Windows Server 2003 sp2 if Protected Mode if OFF and not using Enhanced Security Configuration
  • Internet Explorer 8 on Windows Server 2008 R2 if Protected Mode if OFF and not using Enhanced Security Configuration

5. Non-vulnerable packages

  • Internet Explorer 7 on Windows Vista/Windows Server 2003/Windows 7 if Protected Mode is ON
  • Internet Explorer 8 on Windows Vista/Windows Server 2003/Windows Server 2008 R2/Windows 7 if Protected Mode is ON

6. Vendor Information, Solutions and Workarounds

The vendor has guideance on how to address these vulnerabilities in Microsoft Security Advisory (980088) 

To prevent exploitation of these vulnerabilities the following mitigations are possible:

  • Run Internet Explorer with Protected Mode [3] turned ON if it is supported by the operating system. This is default setting for the Internet security zone on Windows Vista, Windows 7 and Windows Server 2008. Note that there may be specific scenarios where protected mode may need to be turned off [4]
  • Use Internet Explorer's Network Protocol Lockdown feature control to restrict the file: protocol to prevent HTML content from UNC paths from running scripting or ActiveX controls. Note that Network Protocol Lockdown may affect the functionality of Web applications that rely on relaxed security configurations of IE.
  • Set the Security Level setting to High for the Internet and Local Intranet security zones to prevent IE from running scripts or ActiveX controls.
  • Disable Active Scripting for the Internet and Local Intranet zones manually with a custom security setting.
  • Use a different web browser to navigate untrusted web sites.


Additionally, disabling file sharing if it is not necessary and filtering outbound SMB connections at the endpoint or network perimeter are good security measures to prevent disclosure of sensitive information such as valid user, system and domain names that could be used to perform attacks that abuse the vulnerabilities described in this advisory.

7. Credits

These vulnerabilities were discovered and researched by Jorge Luis Álvarez Medina and Federico Muttis from Core Security.

8. Technical Description / Proof of Concept Code

The bugs in this advisory as well as a number of specific methods to combine them with insecure Internet Explorer features are discussed in the paper "Abusing Insecure Features of Internet Explorer". Exploitation of these vulnerabilities as well as others disclosed previously was explained in a presentation at the BlackHat DC 2010 technical security conference

8.1. URLMON sniffing vulnerability

In CoreLabs Security Advisory CORE-2008-0826 [2] a vulnerability that allowed attackers to gain access to any file on the local filesystem of a computer running vulnerable versions of Internet Explorer was disclosed. During the vulnerability reporting process Core provided Proof-of-Concept code to the vendor that successfully exploited the bug on Internet Explorer 8 which at the time was deemed not vulnerable by Microsoft because the bug had been patched prior to RTM. Upon further investigation, the vendor determined that the proof-of-concept provided by Core was actually exploiting a different bug than the one originally reported and therefore it should be considered a separate security issue. The URLMON sniffing vulnerability refers to the variant discovered in the CORE-2008-0826 time line. When loading a local file Internet Explorer's HTML rendering engine [5] will only check its MIME type to see if it is a positive match on the files it can handle. For unknown types that are treated as HTML because they've been referred to by a redirection, content type determination will default to text/html in absence of a type explicitly set by the content source. In the case of non-html files for which there isn't an explicit content-type set, URLMON will default to the text/html type as suggested from the redirection. As a result Internet Explorer will end up loading non-html local files and rendering them as HTML and running any scripting code included in the file in the context of the Security Zone assigned to the content's source.

8.2. Dynamic OBJECT tag vulnerability

Microsoft's June 2009 Cumulative Security Update for Internet Explorer included a patch to fix the bug reported in CORE-2008-0826. The fix was implemented as a modification to the MIME-type detection method when loading content specified in an OBJECT tag. Thus, the contents of the indet.dat file will not be rendered and shown to an Internet Explorer user if it is directly referenced from a webpage with the following HTML code:

 <object data="file://$/.../index.dat" type="text/html" width="100%" height="50" </object> 

However the contents of the same file will be loaded and rendered if the following HTML code is used:

 <script language="Javascript"> var obj = document.createElement("object"); = "file://$/.../index.dat"; obj.type = "text/html"; = "obj_results"; obj.width = "500px"; obj.height = "300px"; document.body.appendChild(obj); </script> 


9. Report Timeline

  • 2009-04-17: Core Security sends proof-of-concept code for the URLMON sniffing vulnerability in IE8 to Microsoft. The code is deemed as an exploit variant for Internet Explorer bug that has already been patched in IE 8 but its part of an ongoing report for other IE versions.
  • 2009-06-01: Microsoft says that the PoC corresponds to a separate bug than the one reported in CORE-2008-0826. On a conference call Core Security Technologies indicates that it considers the bug just a variant of the previously reported one. Microsoft replies that although both cases appear to expose the same functionality the actions are actually controlled by different code and that the differences are significant enough to consider this a separate issue. Microsoft will further investigate and address it in a separate case.
  • 2009-06-10: Cumulative Security Update for Internet Explorer (MS09-019) is published
  • 2009-08-12: Core Security notified Microsoft of the dynamic OBJECT tag vulnerability. Draft advisory sent with publication date scheduled for September 8, 2009.
  • 2009-08-12: Microsoft's MSRC acknoledged the bug report and opened a new case.
  • 2009-08-31: Core asks for an update and reminds MSRC that September 8 2009 is the planned public disclosure date.
  • 2009-08-31: Microsoft replies agreeing that the reported bug is a variant of one previously reported by Core that was fixed in June 2009. Microsof indicates that all the solutions attempted so far did not prove effective and that it currently does not have an update to track towards a fix time. Asks if Core is still on track to disclose it in September 2009.
  • 2009-09-03: Core tells Microsoft that it moved the publication date to October 13 2009 and asks for the complete list of vulnerable platforms. Given that no security fixes for Internet Explorer are planned for September and that the reported bugs are simple variants of others that have been fixed before Core feels confident that the new release date should be appropriate to solve these issues.
  • 2009-09-04: Microsoft thanks Core for postponing publication and says that it is still discussing the fix plan and release date with the IE team and that it will get back to Core in a week with the list of vulnerable platforms and estimated patch release date.
  • 2009-10-09: Received a summary from Microsoft with an update on all open cases with Core. Internet Explorer cases appear listed as "working with product team to determine fix and release date. Earliest potential ship date for a fix is February 2010".
  • 2009-10-23: Core sends email to MSRC indicating that publication of the advisory has been re-scheduled to November 10 2009 and it is open to delaying it further up to the second Tuesday of December 2009 if MSRC is willing to provide: a)detailed technical explanations of the bugs, b)the full list of vulnerable platforms and c)a firm commitment to a release date for the fixes. Core also says that if Microsoft can not target the next IE patch release cycle, Core would rather publish the advisory to let other parties address the risk with alternative fixes or mitigations. The advisory will include the dynamic object tag bug as well as the URLMON sniffing vulnerability from the previous vulnerability report that is pending a fix.
  • 2009-11-02: Update from MSRC saying that it is collecting information and will send a response by Friday Nov. 6.
  • 2009-11-06: Core requests a status update
  • 2009-11-06: MSRC indicates that it will provide an update on Monday Nov. 9
  • 2009-11-09: MSRC sends a status update with detailed descriptions about both bugs, the list of vulnerable platforms and says that it is still working on a tentative fix plan for one of the vulnerabilities. In the case of the other bug, Microsoft is targeting February 2009 to release the fix given that releasing updates in November and December may impact customers due to the typical high e-commerce in those months.
  • 2009-12-12: Core sends email to MSRC saying that advisory publication was now re-scheduled to February 9th, 2010 and asks if Microsoft is on track to release the fixes according to what was stated in previous communications. Core notes that Jorge Luis Alvarez Medina has just received confirmation from the BlackHat Technical Security Conference that his submission for a talk discussing these bugs was accepted. His presentation is scheduled for the first week of February and the advisory publication was re-scheduled to a week after on February 9th assuming that Microsoft will issue patches on the same date.
  • 2010-01-06: Received a summary from Microsoft with an update on all open cases with Core.
  • 2010-01-06: Core reminds MSRC that the advisory disclosing two IE bugs pending resolution will be published on Feb. 9 2010 as noted in an email on December 12 2009.
  • 2010-01-22: Microsoft releases a Cumulative Security Update for Internet Explorer ahead of the regular patch release cycle. The update fixes several bugs but does not include fixes for the two IE cases tracked in this advisory. Core asks MSRC if Microsoft is planning to release another security update for IE during February and indicates that if no further updates are planned Core will publish this advisory simultaneously with the discoverer's presentation at the BlackHat security conference.
  • 2010-01-22: Email from MSRC requesting a conference call to talk about the presentation at the BlackHat DC conference in February
  • 2010-01-25: On a conference call with Core's Security Advisories team, MSRC indicates that fixes for the bugs will be released at some date in the future. Core reminds MSRC that the corresponding security advisory will be published on Feb. 3 on the same date that Jorge Luis Alvarez Medina will disclose details about the bugs and attack vectors at the BlackHat conference. MSRC requests a preview of the presentation slides. Core requests a preview of Microsoft's communciations guidelines regarding Core's upcoming advisory and presentation.
  • 2010-02-02: BlackHat presentation slides sent to MSRC
  • 2010-02-02: Final draft of the advisory sent to Microsoft. Vulnerability identifiers requested from Mitre and
  • 2010-02-03: CoreLabs Security Advisory CORE-2009-0625 published

10. References

[1] CoreLabs Security Advisory CORE-2008-0103 Internet Explorer Zone Elevation restrictions bypass and Security Zone restrictions bypass.
[2] CoreLabs Security Advisory CORE-2008-0826 Internet Explorer Security Zone restrictions bypass.
[3] Understanding and Workiing in Protected Mode Internet Explorer.
[4] Protected Mode for IE7 in Windows Vista - Is it On or Off?
[5] Wikipedia, Trident (layout engine).

11. About CoreLabs

CoreLabs, the research center of Core Security , is charged with anticipating the future needs and requirements for information security technologies. We conduct our research in several important areas of computer security including system vulnerabilities, cyber attack planning and simulation, source code auditing, and cryptography. Our results include problem formalization, identification of vulnerabilities, novel solutions and prototypes for new technologies. CoreLabs regularly publishes security advisories, technical papers, project information and shared software tools for public use at:

12. About Core Security 

Core Security develops strategic solutions that help security-conscious organizations worldwide develop and maintain a proactive process for securing their networks. The company's flagship product, CORE IMPACT, is the most comprehensive product for performing enterprise security assurance testing. CORE IMPACT evaluates network, endpoint and end-user vulnerabilities and identifies what resources are exposed. It enables organizations to determine if current security investments are detecting and preventing attacks. Core Security augments its leading technology solution with world-class security consulting services, including penetration testing and software security auditing.

13. Disclaimer

The contents of this advisory are copyright (c) 2009 Core Security and (c) 2009 CoreLabs, and may be distributed freely provided that no fee is charged for this distribution and proper credit is given.